Fluororesin aqueous dispersions are usually produced by emulsion polymerizing a fluoromonomer in the presence of a fluorosurfactant. Conventional fluorosurfactants are long-chain fluorosurfactants such as perfluorooctanoic acid or its salt (for example, see Patent Literature 1).
However, Patent Literature 2 discloses that the persons and parties involved have proposed to control disposal of ammonium perfluorooctanoate, which does not exist in the natural world and is difficult to decompose, in consideration of the environment, and they also have indicated that the substance is highly bioaccumulative.
Thus, Patent Literature 2 discloses a polytetrafluoroethylene aqueous emulsion obtained by emulsion polymerizing tetrafluoroethylene alone or with a monomer copolymerizable therewith in an aqueous medium using a fluorinated emulsifier represented by the formula (1): XCF2CF2(O)mCF2CF2OCF2COOA (wherein X represents a hydrogen atom or a fluorine atom; A represents a hydrogen atom, an alkali metal, or NH4; and m is an integer of 0 or 1) in an amount of 1500 to 20000 ppm based on the final yield of polytetrafluoroethylene.
For example, Patent Literature 3 discloses a method of producing a low molecular weight polytetrafluoroethylene, comprising emulsion polymerizing tetrafluoroethylene alone or tetrafluoroethylene and a modifying monomer copolymerizable with the tetrafluoroethylene in an aqueous medium in the presence of a reactive compound and a chain-transfer agent, wherein the reactive compound has a hydrophilic group and a functional group that is reactive in radical polymerization, and the amount of the reactive compound is more than the amount corresponding to 10 ppm based on the amount of the aqueous medium.
Further, Patent Literature 4 discloses a method of producing an aqueous dispersion of fluoropolymer particles, comprising the steps of: preparing dispersed particles of a fluorinated ionomer in an aqueous polymerization medium; and polymerizing at least one fluorinated monomer in the presence of the dispersed particles of the fluorinated ionomer and an initiator in the aqueous polymerization medium to form an aqueous dispersion of fluoropolymer particles.